It depends on how you report your efforts. Will you be doing a presentation, formal report, email etc...
If you are reporting it at a high level such as email or powerpoint to higher ups then just display the range of possible savings in whatever unit you desire-- savings per day, week, year...
If you are reporting it as detailed report with technical information then include more about how you derived this savings continuum.
How to guessimate your savings range...
I simplified your formula...
WageSavingsPerDay = AvergaeWageRatePerAction * Executions
Now guess low estimates for hourly wages and how many times you think the query will be executed.
Example Low End: $15/hr, 100 times a day (executions)
AverageWageRatePerAction = $15 * .0583(% of an hour the new query time saves) = .875
therefore the low end would be...
WageSavingsPerDay = .875 * 100 = $87.50
Now repeat for the high end...
Example High End: $25/hr, 165 times a day (executions)
AverageWageRatePerAction = $25 * .0583(% of an hour the new query time saves) = 1.46
Therefore the high end would be...
WageSavingsPerDay = 1.46 * 165 = $240.60
By reducing the query time of x task I have saved the company between $87.50-$240 in wages per day depending on query frequency and wagerates.
Obviously the better information you have regarding wages and query frequency will improve the accuracy of your calculation. This also assumes that people are not productive during the previous duration of the query.
Additionally it should be noted that wages saved may not be the only manner in which a firm would save money.
For example: Reduced query time also reduces CPU usage which also could lower power consumption...etc